Design and research of 1553B bus cable network automatic test system

With the increasing degree of aerospace and electrical integration, the MIL-STD-1553B bus (hereinafter referred to as the 1553B bus) has become increasingly prominent as the preferred data bus for current aerospace electronic equipment, and has been widely used in aerospace, maritime weapons, ground weapons and other fields. As the data bus in satellite/rocket/aircraft/ship/vehicle-borne control systems, the reliability of the 1553B bus cable network directly affects the normal operation of the entire system, and bus failures may even cause incalculable losses. The production and processing of the 1553B bus cable network, as well as the testing of various links before system assembly, are extremely important. Therefore, how to conduct comprehensive and effective testing of the 1553B bus cable network has long been an important topic.
1553B bus cable network

The full name of MIL-STD-1553B bus is: aircraft internal time-division command/response multiplexed data bus, which uses shielded twisted pair to transmit data and transmits signals in the form of serial digital pulses. Its symbol data is represented by biphase Manchester code and the transmission rate is 1Mbit/s. The 1553B bus can connect 32 terminals and adopts command/response communication protocol. There are three types of terminals: bus controller (BC), remote terminal (RT) and bus monitor (BM). The information transmission format is BC to RT, RT to BC, RT to RT, broadcast mode and system control mode. As the transmission medium of 1553B bus data, the 1553B bus cable network is a multi-redundancy bus topology structure, which is connected between various 1553B terminal devices to complete the 1553B protocol data communication. A complete 1553B cable network (as shown in Figure 1) includes the main bus (trunk part), short-circuit wire (branch part connected to each terminal), coupler (connection point between the main bus and short-circuit wire), and terminator (connected to both ends of the main bus).

As the preferred data bus for current aerospace electronic equipment, the national military standard and the US military standard have detailed descriptions on the test and inspection of the 1553B bus. GJB5186.5 and SAE4115 have made relevant specifications for the test standards and methods of the 1553B bus cable network, but the instruments involved are numerous, which is not conducive to comprehensive testing. According to the GJB5186.5, SAE4115 and MIL-STD-1553B standards, the test and inspection of the 1553B bus cable network needs to be carried out: network continuity, network dynamic fault test, network data link integrity test, waveform test - network qualitative analysis, waveform distortion value Vmin, zero-crossing distortion Zcross, waveform symmetry RtZero, etc.

In fact, the test system can be configured as an intelligent 1553B terminal test device. It can be connected to any terminal of the 1553B bus network, and then can work in BC/RT/BM mode at will through software control, and conduct various data communications with all other terminal devices on the bus network, so as to test whether the various functions of the terminal device under test are normal. At the same time, when performing terminal device function tests, the system can inject or detect various communication errors such as data word errors and command word errors, so as to quickly and accurately locate the functional failure of the terminal under test.

1553B Bus Cable Network Automatic Test System

Traditionally, comprehensive testing of 1553B cable network performance parameters requires the use of instruments such as multimeters, characteristic impedance analyzers, oscilloscopes, and time domain reflectometers. The entire testing process is very cumbersome, difficult to implement, and time-consuming. It is difficult to form a unified test report, and the efficiency and reliability are very low. [page]

The 1553B bus cable network automatic test system effectively solves the above problems. It can perform comprehensive quantitative and qualitative test analysis on the 1553B bus cable network. The whole process is completed automatically without manual intervention, and finally a detailed test analysis report is formed, which can greatly improve the test efficiency and reliability.

System Design

This system adopts a cabinet structure and modular design, mainly including a system human-computer interaction interface, a system control processor, a 1553B bus test dedicated controller (to achieve standard 1553B bus signal excitation source, test auxiliary analysis and test switching control, etc.), a data acquisition module, a test interface panel (to achieve access to the network under test) and a printer (to print test result reports). Figure 2 is a functional block diagram of the entire system.

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System function modules

Some modules of this system can be implemented directly using existing modules. Among them, the system control processor, which is responsible for the entire system test control process, data analysis, algorithm implementation, etc., is implemented using an industrial computer with good stability; the human-computer interaction part is implemented in conjunction with the industrial computer using a LCD display, keyboard, mouse, and printer (to print out the test result report), and combined with the test interface software; the data acquisition and impedance analysis modules are implemented using a digital oscilloscope with a programming interface.

Dedicated test controller

The 1553B bus cable network dedicated test controller has two major functions: as a signal source for cable testing, it generates standard 1553B digital signals and sine wave and other excitation signals for testing; it completes the switching of signal source input and signal acquisition terminal during the test. The functional block diagram of the dedicated test controller is shown in Figure 3.

The processor system module and the 1553B bus signal source controller module are implemented in the form of FPGA Cyclone III EP3C55F484 loaded with S698 IP core + 1553B IP core. The S698 IP core independently developed by Zhuhai Orbit is a scalable core based on the AMBA bus architecture. It has rich peripherals on the chip and has good reliability. It has been widely used in the aerospace field. The 1553B IP core is also a bus controller module that complies with the 1553B protocol developed by Orbit specifically for equipment in aviation and aerospace measurement and control networks. The module implements the 1553B bus protocol processor and bus data transceiver internally, and can complete the functions of three bus devices: bus controller (BC), remote terminal (RT) and bus monitor (BM). Here, both the S698 IP core and the 1553B IP core are scalable, and their functions can be increased or reduced according to the needs of the test system. The 1553B soft core implements the hardware analysis of the entire MIL-STD-1553B bus protocol inside the FPGA, but the logic conversion and drive of the 1553B signal level need to be implemented externally through the transceiver driver. Here, HOLT's 1553B bus transceiver driver HI-1573 is selected for design.

Taking into account the functional requirements of the system, the program memory uses SST's 8-bit FLASH, model 39VF040 (512×8bit), and the address range of the processor occupied is: 0x0000000~0x0007ffff; the data memory uses ISSI's 16-bit SRAM, model IS61LV51216 (512×16bit), and the address range of the processor occupied is: 0x4000000~0x400fffff.

The channel switching module mainly completes the selective input of the excitation signal to the network under test and the selective collection of the data signal on the network under test. Therefore, the switch used to select the conduction must have the characteristics of small on-resistance and small on-capacitance, so as to greatly reduce the influence of the switch on the excitation signal or the collected signal. Taking all factors into consideration, Omron relays were selected for design.

In order to maximize compatibility with the access test of the universal 1553B bus cable network, the interface panel is designed according to the requirements of accessing 32 1553B bus cable network endpoints. At the same time, each set of connectors consists of 1 female (DK-621-0940-4S) and 1 male (DK-621-0940-4P) sockets to be compatible with external male (DK-621-0939-4P) and female plugs (DK-621-0939-4S).